Variable resistance device



Jan. 12, 1965 C. A. MOUNTEER VARIABLE RESISTANCE DEVICE 2 Sheets-Sheet 1 Filed March 14, 1965 INVENTOR.

QALVLE A Maw/WEE? 7 Jan. 12, 1965 c. A. MOUNTEER 3,165,713

VARIABLE RESISTANCE DEVICE Filed March 14, 1963 2 Sheets-Sheet 2 alrw4.

QRLYLEA. Mod/W254;

INVENTOR.

BY #1.; Irma/V5515 United States Patent 3,165,713 VARIABLE RESISTANCE DEVICE Carlyle A. Mounteer, 1250 Sierra Madre Villa, Pasadena, Calif. Filed Mar. 14, 1963, Ser. No. 265,183 9 Claims. (Cl. 33 815l This invention relates to improved and novel variable resistance device structures. Present art variable resistance devices commonly employ an electrical contact which is movable in response to an applied force, the movement being along a resistance path defined on the surface of a resistance body. The adjusting force which causes the variation in the effective resistance of the device may be manually applied, such as in potentiometers and rheostats, or mechanically applied, such as in pressure transducers and accelerometers.

In certain applications, it is important that a variable resistance device of a given total resistance have high resolution, i.e., a small change'in effective resistance per given change in adjustment. Certain variable resistance devices, particularly the wire wound types in which the effective resistance is varied in single turn increments, are characterized by inherently poor resolution. Better resolution can be provided by forming the resistance body of a greater number of turns of lower resistance wire so that the single turn increment in resistance is decreased. However, a bulkier and more cumbersome device results since it is still necessary to be able to establish separate electrical contact to each turn of the resistance winding. The present invention is directed toward improvement of the resolution of variable resistors, particularly of the wire wound type.

In certain applications, it is desirable-to use a variable voltage divider or potentiometer in which the output voltage is some nonlinear function of the adjusting force. Such devices are relatively easy to fabricate using composition resistors as the resistance bodies, and such devices provide adequate resolution. However, there is a present need in the art for a functionalized output voltage divider of greater power handling capabilities, and greater ruggedness and reliability than provided by the aforementioned composition type otentiometers. The present invention is also directed toward fulfillment of this need by providing a wire wound, functionalized output, voltage divider of high resistance resolution.

Accordingly, it is an object of the present invention to provide improved variable resistance device structures.

It is also an object of the present invention to provide improved variable resistance device structures characterized by high resistance resolution.

It is another object of the present invention to provide wire wound variable resistance devices characterized by high resistance resolution.

It is a further object of the present invention to provide improved wire wound variable resistance devices characterized by smoothness of operation.

It is yet another object of the present invention to provide improved variable resistance device structures characterized by high reliability and precision of adjustment.

It is a. still further object of the present invention to provide improved variable voltage divider structures.

It is also an object of the present invention to provide wire wound variable voltage divider structures having an output which is a predetermined linear or nonlinear function of the adjusting force.

The objects of the present invention are generally accomplished by a variable resistance device structure in which elongate resistance members are disposed in angular relationship and in surface contact with each other. Relative movement of the members, while still maintainice i-ng the angular relationship and surface contact between them, provides a variation in the effective resistance of the device, as appearing between an end of each of the resistance members, together with high resistance resolution. Two angularly disposed resistance members provide a simple rheostat function, while two sets of such rheostats connected in series will provide a voltage divider or potentiometer in which the output voltage can be made a predetermined function of the adjusting force.

The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and ad vantages thereof, will be better understood from the following description considered in connection with the accompanying drawings in which various embodiments of the invention are illustrated by way of example. Due to the particularly advantageous application of the present inventive concepts to variable resistors of the wire wound type, the illustrated embodiments will be of this type. It is to be expressly understood, however, that the drawing is for the purpose of illustration and description only, and is not intended as a definition of the limitsof the invention.

In the drawing:

FIGURE 1 is a perspective view showing the basic variable resistance device in accordance with the present invention concepts, the device being shown in a low resistance position;

FIGURE 1a is a schematic diagram illustrating the low effective resistance of the device in the position of FIGURE 1; I

FIGURE 2 is a perspective View showing the basic device of FIGURE 1 in a high resistance position;

FIGURE 2a is a schematic diagram illustrating the high effective resistance of the device in the position of FIGURE 2;

FIGURE 3 is aschematic diagram showing the use of the present invention concepts to provide a functional output variable voltage divider; 1

FIGURE 4 is a view of a practical embodiment of the variable voltage divider of FIGURE 3, as used in a pressure transducer, the view being taken along the line 4-4 of FIGURE 5;

FIGURE 5 is a view taken along the line 5-5 of FIGURE 4;

FIGURE 6 is a perspective view showing details of the mounting of a shaft in the embodiments of FIGURES 4 and 5; and,

FIGURE 7 is an enlarged fragmentary view showing one of the shafts in a partial rotated position, together with a vectorial representation of various loading forces.

As indicated hereinabove, the common prior art variable resistance devices utilize a movable metallic member to establish electrical contact along a resistance path defined on the surface of a resistance member, the effective resistance of the device appearing between the metallic contact and one end of the resistance path. The present invention concept, on the other hand, is to utilize two elongate resistance members disposed in angular relationship with portions of their surface resistance paths in contact with each other. Thus, surface contact is with another resistance member rather than with a metallic electrical contact, the effective resistance of the device appearing between an end of each of the resistance members. This basic configuration is illustrated in FIGURES 1 and 2 of the drawing.

In FIGURE 1 of the drawing, there are shown two elongate resistance members, generally indicated by the reference numerals 1t and 26. The resistance member 10 comprising a cylindrical form of insulating material 11 upon which is Wound resistance wire to form a helical coil 12, the resistance member 263 comprising a cylindrical form of electrical insulating material 21 upon which is wound resistance wire to form a helical coil 22;. The sum of the resistances of the helical coils l2 and 22 determines the maximum device resistance. One end of the resistance Wire Winding of the coil 12 terminats at an electrical contact 15 mounted at the end of the form 11, one end of the resistance wire of the coil 22 terminating at an electrical contact 25 mounted at the end of the form 21. Electrical lead wires 16 and 26 provide respective electrical connection of the terminals 15 and 25 to external electrical circuitry in which the variable resistance device is to be used.

In the embodiment shown in FIGURE 1 the device is intended for use as a simple two-terminal rheostat, the effective resistance of the device appearing between the electrical leads l6 and 26. Thus, in the position shown in FIGURE 1 the effective device resistance is quite low, as can be seen by reference to the schematic diagram of FIGURE la. In this embodiment the effective resistance of the device is that portion of the resistance of the member Ztl extending from electrical terminal 25 to the point of contact with the member 1i plus that portion of the resistance of the member W from the point of contact to the electrical terminal I5. With the resistance members in the position shown in FIGURE 1 the total resistance path is relatively short and the effective resistance quite low.

The resistance members iii and 2d are shown in FIG- URE 1 as disposed in an angular relationship, the acute angle between them being designated by the reference character (p. It is readily apparent that if the resistance members are moved away from each other, while still maintaining their angular relationship and contact between their surface resistance paths, the point of contact between them will move generally upwards, thereby increasing the length of the effective resistance path between the electrical leads 16 and 26. Now if the resistance members are moved away from each other along a linear path which is perpendicular to the bi'sector of the angle (1), i.e., such that the locus of a givenidentical point on each of the resistance'members is a line perpendicular to the bisector of the acute angle, the point of contact will move through a distance greater than the movement of the given point of either member. Thus, when the resistance members are moved in this manner, the contact point between them will move the distance of a given point on the member multiplied by the secant of 2, thereby increasing the resistance resolution of the device. Furthermore, the angle g can be chosen and the direction of winding of the helical coils can be chosen so that a combination of coil turns are in contact, the contact resistance at the marginal contacting turns being different than the contact resistance of the central contacting turns. Thus, the turn resistances and contact resistances appear as a complex of parallel resistances and the variation in resistance as the two coils are moved will be less than the amount of resistance change expected from discrete increments of single turns, thereby further improving the resistance resolution of the device. the angle will provide different rates of resistance change, as will winding of the forms 11 and 2,1 with wire of different resistivity. The resistance change rate can.

also be altered by using curved forms instead of the straight cylindrical forms 11 and 21 so that the helical coils will be curved.

FIGURE 2 of the drawing shows resistance members and 20 of FIGURE 1 upon movement away from each other to thereby increase the effective resistance of the device, the schematic diagram of the device in this new position being shown in FIGURE 2a. In the position of FIGURE 2 the effective length of the resistance path between the electrical leads 61 and 26 has been increased to the extent that almost the entire length of each of the Also, variation of resistance members contributes to the total resistance. It is readily apparent that if the resistance members are moved even farther away from each other, so that uppermost end turns of each of the resistance members are in contact, then the maximum resistance will be attained.

Since the contacting surfaces of the wire wound resistance members are irregular rather than planar it would appear that relative movement of the two members would be fairly rough, movement over each particular turn of wire being in an arcuate .path. However, it has been found that when the angle e is made substantially less than 90, -the turns of wire ride on one another in such a manner that substantially smooth movement results. And if the angle is made equal to the sum of the helix angles of the two coils, maximum smoothness and resolution is achieved.

Since closely wound coils contribute toward maximum resolution and smoothness of operation, it is presently preferred to use resistance wire which has been enameled or otherwise coated with a thin film of electrical insulating'material. The enamel is thenremoved in a linear path along the coil surface to define the surface resistance path of the resistance member. Those skilled in the art will appreciate that, depending upon the environment in which the device is to be used, friction, desired life, etc., it may be desirable in some applications to make the helical coils of cooperating resistance members of different diameter and/ or to wind them with resistance wire of differing resistivity, diameter or material. Also, the resistance members can be of any form in which a longitudinally extending exposed surface area defines a resistance path. For example, carbon rods may be used as the resistance member to provide a linear resistance or, alternatively, a series of carbon discs of the same diameter, but of different resistance can be used to form a straight resistance member having a non-linear resistance path.

The hereinabovedescribed embodiment shown in FIG- URES 1 and 2 of the drawing illustrates application of the present inventive concepts to a simple two terminal rheostat type of variable resistance device. ture .can be utilized to provide three and four terminal devices of more complex resistance variation merely by providing electr-ical terminals at both ends of each helical resistance coil. Furthermore, two of the illustrated two terminal rheostats may be arranged in series to provide a variable voltage divider or potentiometer, the output of which may be made any of various functions of changes in adjustment. In FIGURE 3 of the drawing, there is shown a schematic diagram depicting such a variable voltage divider. The voltage divider consists of a first pair of cooperating resistance members 31 and 32, mechanically coupled with a second pair of cooperating resistance members 33 and One end of the resistance member 32 is connected to an end of the resistance memvoltage (B being taken between one end of the re sistance member 311 and the electrical lead 36. The re sistance member 31 is mechanically coupled to the resistance member 33 for movement in unison therewith, the resistance members 32 and 34 being similarly mechanically intercou-pled for unitary movement. Again, the relative movement of cooperating resistance members is such as to maintain surface contact between them and preserve their relative angular relationships in the hereinabove-described manner.

If the resistances of each of the resistance members 31-34 are respectively designated R R32, R and R the output of the voltage divider of FIGURE 3 can be expressed as Rides;

This basic strucwhich is a family of hyperbolas.

Ravi-R34 a linear output is provided. Thus, it can be seen that by proper choice of the resistance values of the resistance members 3144, the voltage divider output can be made linear or functionalized in various non-linear manners.

In FIGURES 4-7 of the drawings, there is disclosed a practical embodiment of a variable voltage divider of the type shown in FIGURE 3, as used in a pressure transducer. The resistance members are generally indicated by the reference numerals 31-34, corresponding with those indicated schematically in the diagram of FIGURE 3. The resistance members 31 and 33 are secured to a mounting plate 41 by means of angle brackets 42 and 43, each of the resistance members being mounted at one of its ends to the associated mounting bracket. In a similar manner, the resistance members 32 and 3d are secured to a mounting plate 46 by means of angle brackets 47 and 4-8. The angle brackets are disposed on their respective mounting plates at one half of the angle (35 chosen for the angular relationship of the resistance members in the device. The mounting plates holding the resistance members are mounted to a coupling structure which maintains the resistance members in the desired relationship and mechanically couples them for movement to the force-summing diaphragms of the transducer.

The coupling structure generally consists of a pair of endless belts 51 and 52 looped around a pair of identical elongate forms, generally indicated by the reference numerals 60 and 80, each belt defining a pair of parallel belt runs extending between the elongate forms. The endless belts may be loops formed of flexible materials such as leather, fabric, plastic, etc., as well as chains, cables or other forms of flexible loop structures using rigid materials alone or in combination with flexible materials.

As can best be seen from FIGURE 6 of the drawings, the elongate form 60 include a cylindrical shaft 61 provided with radially extending end portions 62 and 63, the end portions 62 and 63 defining circumferential shoulders. A third radially extending projecting portion, generally indicated by the reference numeral 64, is provided intermediate the ends to define a third circumferential shoulder. A rectangular support block 66 is rigidly mounted to the end portion 62, in a position displaced from the central axis of the shaft 61 and extending transversely thereto. A rectangular support block 67 is similarly rigidly mounted to the other end portion 63. A rectangular mounting block 71 i secured to the support block 66 by means of a pair of offset leaf springs 72 and 73, the opposing end portions of the leaf springs 72 and 73 being rigidly secured to the respective mounting and support blocks 71 and 66 to assume the illustrated crossed angular relationship in the absence of any applied torsional forces. The mounting block 71 is slightly spaced away from the end portion 62 of the shaft 61 so that the form 60 can be rotated with respect to the mounting block 71 in accordance with flexure of the leaf springs 72 and 73, as will be explained hereinbelow. A mounting block 76, similar to the mounting block 71, is similarly secured to the support block 67 by a pair of offset leaf springs 77 and 78, the mounting block 76 being spaced slightly away from the end portion 63 of the shaft 61 to permit rotation of the form 60 with respect to the mounting block 76. The details of the mounting of the blocks 71 and 76 can best be seen in FIGURES 4, S and 6. The form 80 is identical in construction to the form 60, the cylindrical shaft 81 of the form 80 being provided with radially projecting end portions 82 and 83 and an intermediate circumferential shoulder 84. Support blocks 86 and 87 are mounted respectively to the end portions 82 and 83. A rectangular mounting block 91 is secured to the support block 86 by means of offset leaf springs 92 and 9 3, a similar mounting block 96 being secured to the support block 37 by means of offset leaf springs 97 and 98. The mounting blocks 91 and 96 are spaced slightly away from the end portions of the form 89 to allow rotation of the form with respect thereto upon bending of the leaf springs.

The forms 66 and 86 are rotatably mounted to a supporting framework Mill, indicated by the fragmentary shaded portions in FIGURE 4, by rigid securement of the mounting blocks 71, '76, 91 and 96 to the supporting framework 11 0. The supporting framework 106 may be of any desired form defining spaced apart surfaces for the mounting of the forms 66 and therebetween. The endless belt 51 is looped over the end portions 63 and 33 of the respective shafts 61 and 81, while the endles belt 52 is looped over the end portions 62 and 82 of the respective shafts 61' and 81. The mounting plate 41, containing the resistance members 31 and 33, is secured to the lowermost belt run of the endless belt 51 by means of large area retaining nut 53 and 54 threaded onto screws projecting from the mounting plate 41. Thus, the belt 51 is clamped between the mounting plate 41 and portions of the retaining nuts 53 and 54. In a similar manner, the mounting plate 46 is secured to the uppermost belt run of the endless belt 52 by means of large area retaining nuts 56 and 57 threaded onto screws projecting from the mounting plate.

The diameter of the end portions of the forms 60 and 81B are smaller than the spacing between the mounting plates 41 and 46 when the mounting plates are clamped into position on their respective endless belts. Therefore, as can best be seen in FIGURE 7, the upper and lower portions of the belt runs will not be exactly parallel to each other near their points of initial and terminal contact with the end portions of the forms, thereby resulting in a force component transverse to the belt run to urge the resistance members into surface contact with each other. In practice, the spacing between the mounting plates 41 and 46 can be made adjustable, such as for ex ample by adjustable mounting of the resistance members to the angle brackets, in order to provide adjustment of the contact force in a manner to be explained hereinbelow.

In the pressure transducer of the illustrated embodiment, the force summing means of the transducer are pressure diaphragms, generally indicated by the reference numerals 101 and 102. The diaphragm 161 is coupled by means of a pressure inlet 1113 to the source of pressure from which is derived the mechanical input to the variable resistance device. The diaphragm 102 i also coupled to the same source of pressure through a pressure inlet 104. One end of a metallic coupling strip 167 is secured to the diaphragm 1111, the other end of the coupling strip being tangentially secured to the intermediate circumferential shoulder 64 of the form 611. One end of a metallic coupling strip 167 is fastened to the diaphragm 102, the other end of the coupling strip being tangentially secured to the intermediate circumferential shoulder 84 of the form 80. Thus, movement of the diaphragm 101, in response to variations in applied pressure, will exert a force on the form 61) which tends to rotate it about its mounting blocks 71 and 76. Similarly, variations in applied pressure will cause movement of the diaphragm 102 to thereby exert a force on the form 86 which tends to rotate the form about its mounting blocks 91 and 96.

In FIGURES 4 and 5 of the drawing, the apparatu is shown with atmospheric pressure applied to the diaphragms 161 and 1112. Thus, application of additional pressure to the diaphragms will cause the forms 69 and 811 to rotate in a clockwise direction, causing movement of the resistance members 32 and 34 toward the form 81) and movement of the resistance member 31 and 33 to- 'belt as it runs over the edge of the mounting plate.

ward the form as. The mounting blocks 91 and 96 are rigidly mounted to the frame Md and hence cannot rotate. However, the application of a tangential force to the intermediate circumferential shoulder 84 on the shaft 81 will cause flexure of the leaf springs 92, 93, 97 and 98 by which the shaft 81 is secured to the blocks 91 and 96, and rotation of the shaft will result. Similarly, the application of the tangential force to the intermediate cir cumferential shoulder M on the shaft 61 will cause fiexure of the leaf springs 72, 73, '77 and '73 by which the shaft at is secured to the blocks '71 and 76, and rotation of the shaft will result. Variations in the pressure applied to the diaphragms will then vary the tangential forces applied to the cylindrical shafts and so cause varying degrees of rotation of these shafts, together with corresponding movements of the mounting plates 41 and 46 attached to the endless belts which are looped around the shafts.

The illustrated-method of rotatably mounting the cylindrical shafts by means of crossed-flexurc pivots is presently preferred because of the operational advantages which can be derived therefrom. More particularly, the

supporting framework Mitt is made selectively adjustable so that the distance between the cylindrical shafts 61 and 81 can be increased to the point where the endless belts 51 and 52 are tightly'stretched over the forms to provide preloading of the leaf spring ilexure pivots in compression to thereby reduce the spring rate to substantially zero while imposing a proper contact force between the resistance members. The leaf springs are preloaded in compression by a hinge load force, represented by the vector.

111 in FIGURE 7, this hinge-load force being achieved by proper adjustment of the spacing between the cylindrical shafts til and 81. Further reference to FIGURE 7 shows that the hinge-load force vector ililit is horizontally directed due to the hinge effect created by bending of the The vector 112 represents the band tension and is inclined downward below the horizontal by an angle a due to spacing of the mounting plates apart a distance greater than the diameter of the end portions of the cylindrical forms, this spacing also providing the desired contact force as represented by the vertically directed vector 113. In adjustment of the device, the hinge-load force is chosen to reduce the spring rate to zero and the angle or is chosen to result in the desired contact force, a contact force of from about 3 to 10 grams being presently preferred. The compression loading of the springs by the horizontally directed hinge-load force is balanced by an equal spring restoring force which reduces the applied force necessary for rotational deflection of the springs, thereby resulting in a reduction in the effective spring rate. Thus, by proper selection of the hinge-load force, a zero residual spring rate load can be closely approached with a minimum of mechanism backlash and the attendant increase in device sensitivity.

It will be readily apparent to those skilled in the art that other force-summing means may be substituted for the diaphragms shown in the illustrated embodiment to cause a variation in the effective resistance of the device, which is thus a measure of the force imposed. The forcesumming means may be rods, bellows, weights, or any other members subiect to motion in space as a result of the forces imposed thereon. The force-summing means is a medium for summing of applied forces and transmitting the summed forces to the resistive members. Through the use of appropriate force-summing means,

the transducer may be'used to measure such phenomena as displacement, pressure, velocity and acceleration. Furthermore, there are many other possible structural ar-' hereinafter claimed.

What is claimed is: l. A variable electrical resistance device comprising: (a) first and second elongate resistance members each having a longitudinally extending exposed surface area defining a rectilinear resistance path along which the resistance of the member is evenly distributed in predetermined substantially equal increments, said members being disposed with their resistance paths in a predetermined acute angular relationship andv with a portion of their respective resistance paths in surface contact with each other; and,

(b) means for selectively moving said resistance members relatively to each other while maintaining said predetermined angular relationship and surface'contact between said resistance paths, the movement of each of said members being along a linear path perpendicular to the bisector of theacutc angle between the resistance paths so that the point of surface contact simultaneously varies along each of said resistance paths to thereby vary the effective resistance between one end of the resistance path of said first member and one end of the resistance path of said second member.

2. A variable electrical resistance device comprising:

(a) first and second elongate resistance members each having a longitudinally extending exposed surface area defining a rectilinear resistance path along which the resistance of the member is evenly distributed in identical predetermined substantially equal increments, said members being disposed with their resistance paths in a predetermined acute angular relationship and with corresponding increments of their respective resistance paths in surface contact with each other; and,

(b) means for selectively moving said resistance members relatively to each other at an identical rate while maintaining said predetermined angular relationship and surface contact between said resistance paths, the movement of each of said members being along a rectilinear path perpendicular to the bisector' tudinally extending resistance path along which the resistance of the member is evenly distributed in single turn increments, said members being disposed in a predetermined acute angular relationship substantially equal to the sum of the helix angles of said first and second resistance members and with a portion of their respective resistance paths in surface contact with each other; and,

(b) means for selectively moving said resistance members relatively to each other while maintaining said predetermined angular relationship and surface contact between them, the movement of each of said members being along a linear path perpendicular to the bisector of the acute angle between the members so that the point of surface contact simultaneously varies along each of said resistance paths to thereby vary the effective resistance between one end of the resistance wire of said first member and one end of the resistance wire of said second member.

4. A variable electrical resistance device comprising:

(a) first and second identical elongate resistance members each consisting of a length of resistance wire helically wound on the peripheral surface of an elongate rectilinear support member with corresponding exposed surface portions of the Wire turns defining a longitudinally extending resistance path along which the resistance of the member is evenly distributed in single turn increments, said members being disposed in a predetermined acute angular relationship substantially equal to the sum of the helix angles of said first and second members and with a portion of their respective resistance paths in surface contact with each other; and,

(b) means for selectively identically moving said resistance members relatively to each other while maintaining said predetermined angular relationship and surface contact between them, the movement of each of said members being along a linear path perpendicularto the bisector of the acute angle between the members so that the point of surface contact simultaneously varies along each 'of said resistance paths to thereby vary the effective resistance between one end of the resistance wire of said first member and one end of the resistance Wire of said second member.

5. A variable voltage dividing device comprising:

'(a) first, second, third and fourth elongate resistance members each consisting of a length of resistance wire helically wound on the peripheral surface of an elongate rectilinear support body with corresponding exposed surface portions of the Wire turns defining a longitudinally extending linear resistance path along which the resistance of the member is evenly distributed in single turn increments, said first and second members being disposed in a predetermined acute angular relationship with a portion of their respective resistance paths in surface contact with each other, said third and fourth members being disposed in said predetermined acute angular relationship with a portion of their respective resistance paths in surface contact with each other; (Z1) means for selectively moving said first and second resistance members relatively to each other while maintaining said predetermined angular relationship and surface contact between them and for simultaneously selectively moving said third and fourth resistance members relatively to each other while maintaining said angular relationship and surface contact between them, the movement of each of said members being along a linear path perpendicular to the bisector of the acute angle between said first and second resistance members so that the points of surface contact between said first and second members and between said third and fourth members simultaneously vary along each of said resistance paths to thereby vary the ratio of the effective resistance between one end of the resistance Wire of said first member and said interconnecting means relative to the effective resistance between said one end of the resistance wire of said first member and one end of the resistance wire of said fourth member; and means electrically interconnecting one end of the resistance wire of said second member and one end of the resistance wire of said third member.

6. A variable resistance device comprising:

(a) support means defining ltwo spaced apart pairs of mounting blocks;

(b) a coupling structure rotatably secured to said support means, said coupling structure including a pair of endless belts looped around first and second spaced apart elongate forms, each belt defining uppermost and lowermost parallel belt runs extending between said first and second forms, each of said first and second forms being disposed between a different pair of said mounting blocks and rotatably secured thereto;

(c)v first and second elongate resistance members each having a longitudinally extending exposed surface area defining a resistance path, said first resistance member being secured to the uppermost belt run of one of said endless belts and extending toward the other endless belt, said second resistance member being secured to the lowermost belt run of said other endless belt and extending toward said one endless belt, said resistance members being disposed in angular relationship with a portion of their respective resistance paths in surface contact with each other; and,

(d) means for simultaneously rotating said first and second elongate forms in the same direction in response to an applied'actuating force to cause movement of said belt runs and of said resistance members while maintaining said relative angular relationship and surface contact between them to thereby vary the effective resistance between one end of the resistance path of said first member and one end of the resistance path of said second member.

7. A variable resistance device comprising:

(a) support means defining two spaced apart pairs of mounting blocks;

(b) a coupling structure rotatably secured to said support means, said coupling structure including a pair of endless belts looped around first and second spaced apart elongate forms, each belt defining uppermost and lowermost parallel belt runs extending between said first and second forms, each of said first and second for-ms being disposed between a different pair of said mounting blocks and rotatably secured thereto;

(0) first and second elongate resistance members each consisting of a length of resistance wire helically wound on the peripheral surface of an elongate support member with corresponding exposed surface portions of the wire turns defining a longitudinally extending resistance path along which the resistance of the member is distributed in single turn increments, said first resistance member being secured near one of its ends to the uppermost belt runs of one of said endless belts with its resistance path facing downwardly and extending toward the other endless belt, said second resistance member being secured to the lowermost belt run of said other endless belt with its resistance path facing upwardly and extending toward said one endless belt, said resistance members being disposed in a predetermined angular relationship with a portion of their respective resistance paths in surface contact with each other; and

(d) means for rotating said first and second elongate forms in unison inresponse to an applied actuating force to move said belt runs and said resistance members while maintaining said predetermined angular relationship and surface contact between them to thereby vary the effective resistance between one end of the resistance wire of said first resistance member and one end of the resistance wire of said second resistance member.

8. A variable resistance device comprising:

(a) support means defining two spaced apart pairs of mounting blocks;

(b) a coupling structure rotatably secured to said support means, said coupling structure including apair of endless belts looped around first and second 1 1 spaced apart elongate forms, each belt defining uppermost and lowermost parallel belt runs extending between said first and second forms, each of said first and second forms being disposed between a differ- "i2 and lowermost parallel belt runs extending between said first and second forms, each of said first and second forms being disposed between a diiferent pair of said mounting blocks and rotatably secured thereent pair of said mounting blocks and rotatably se- 5 to; V cured thereto at each end of the form by a pair of off- (0) first, second, third and fourth elongate resistance set crossed leaf springs, one end of each of said leaf members, each having a longitudinally extending exsprings being secured to a mounting block and the posed surface area defining a resistance path, said other end secured to an end portion of a form; first and third resistance members being secured to (c) first and second elongate resistance members each the uppermost belt run of one of said endless belts consisting of a length of resistance wire helically and extending toward the other endless belt, said wound on the peripheral surface of an elongate supsecond and fourth resistance members being secured port member with corresponding exposed surface porto the lowermost belt run of said other endless belt tions of the wire turns defining a longitudinally exand extending toward said one endless belt, said first tending resistance path along which the resistance of and second resistance members being disposed in a the member is distributed in single turn increments, predetermined angular relationship with a portion of said first resistance member being secured near one their respective resistance paths in surface contact .of its ends to the uppermost belt runs of one of with each other, said second and fourth resistance saidtendless belts with its resistance path facing downmembers being disposed in said predetermined anguwardly and extending toward the other endless belt, lar relationship with a portion of their respective resaid second resistance member being secured to the 'sistance pathsin surface contacts with each other; lowermost belt run of said other endless belt with I (a!) means electrically interconnecting one end of the its resistance path facing upwardly and extending to resistance path of said second resistance member and ward said one endless belt, said resistance members one end of the resistance path of said third resistance being disposed, in a predetermined angular relationem er; and ship with a portion of their respective resistance (8) means for rotating said first and second elongate paths in surface contact with each other; and forms in unison in response to an applied actuating (d) means for simultaneously rotating said first and force to thereby move said first and second resistance second elongate forms in response to an applied acmembers relatively to each other while maintaining tuating force to move said belt runs and said resistthe predetermined angular relationship and surface ance members while maintaining said predetermined contact between them and simultaneously moving angular relationship and surface contact between said third and fourth resistance members relatively them to thereby vary the efiective resistance between to each other while maintaining the angular relationone end of the resistance wire of said first resistance ship and surface contact between them whereby the member and one end of the resistance wire of said effective resistance between one end of the resistance second resistance member. path of said first member and said interconnecting 9. A variable wire wound potentiometer device commeans is varied relatively to the effective resistance prising: between said one end of the resistance path of said Support means d fi i two spaced apart pail-S f first member and the other end of the resistance path mounting k 4 of said fourth member.

(b) a coupling structure rotatably secured to said support means, said coupling structure including a pair of endless belts looped around first and second spaced apart elongate forms, each belt defining uppermost Referrer: es Cited in the file of this patent UNITED STATES PATENTS 728,978 Reed May 26, 1903 

1. A VARIABLE ELECTRICAL RESISTANCE DEVICE COMPRISING: (A) FIRST AND SECOND ELONGATED RESISTANCE MEMBERS EACH HAVING A LONGITUDINALLY EXTENDING EXPOSED SURFACE AREA DEFINING A RECTILINEAR RESISTANCE PATH ALONG WHICH THE RESISTANCE OF THE MEMBER IS EVENLY DISTRIBUTED IN PREDETERMINED SUBSTANTIALLY EQUAL INCREMENTS, SAID MEMBERS BEING DISPOSED WITH THEIR RESISTANCE PATHS IN A PREDETERMINED ACUATE ANGULAR RELATIONSHIP AND WITH A PORTION OF THEIR RESPECTIVE RESISTANCE PATHS IN SURFACE CONTACT WITH EACH OTHER; AND, (B) MEANS FOR SELECTIVELY MOVING SAID RESISTANCE MEMBERS RELATIVELY TO EACH OTHER WHILE MAINTAINING SAID PREDETERMINED ANGULAR RELATIONSHIP AND SURFACE CONTACT BETWEEN SAID RESISTANCE PATHS, THE MOVEMENT OF EACH OF SAID MEMBERS BEING ALONG A LINEAR PATH PERPENDICULAR TO THE BISECTOR OF THE ACUTE ANGLE BETWEEN THE RESISTANCE PATHS SO THAT THE POINT OF SURFACE CONTACT SIMULTANEOUSLY VARIES ALONG EACH OF SAID RESISTANCE PATHS TO THEREBY VARY THE EFFECTIVE RESISTANCE BETWEEN ONE END OF THE RESISTANCE PATH OF SAID FIRST MEMBER AND ONE END OF THE RESISTANCE PATH OF SAID SECOND MEMBER. 